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Message-ID: <20170228075305.GA8775@gmail.com>
Date: Tue, 28 Feb 2017 08:53:05 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Josh Poimboeuf <jpoimboe@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [GIT PULL] objtool fixes
Linus,
Please pull the latest core-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-urgent-for-linus
# HEAD: 4e4636cf981b5b629fbfb78aa9f232e015f7d521 objtool: Enclose contents of unreachable() macro in a block
A handful of objtool fixes related to unreachable code, plus a build fix for out
of tree modules.
Thanks,
Ingo
------------------>
Josh Poimboeuf (4):
objtool: Fix CONFIG_STACK_VALIDATION=y warning for out-of-tree modules
objtool: Improve detection of BUG() and other dead ends
objtool: Prevent GCC from merging annotate_unreachable()
objtool: Enclose contents of unreachable() macro in a block
Makefile | 24 ++++++++---------
arch/x86/kernel/vmlinux.lds.S | 1 +
include/linux/compiler-gcc.h | 14 +++++++++-
tools/objtool/arch.h | 5 ++--
tools/objtool/arch/x86/decode.c | 3 ---
tools/objtool/builtin-check.c | 60 ++++++++++++++++++++++++++++++++++++++---
6 files changed, 84 insertions(+), 23 deletions(-)
diff --git a/Makefile b/Makefile
index f1e6a02a0c19..32c84577aa93 100644
--- a/Makefile
+++ b/Makefile
@@ -908,6 +908,18 @@ mod_sign_cmd = true
endif
export mod_sign_cmd
+ifdef CONFIG_STACK_VALIDATION
+ has_libelf := $(call try-run,\
+ echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)
+ ifeq ($(has_libelf),1)
+ objtool_target := tools/objtool FORCE
+ else
+ $(warning "Cannot use CONFIG_STACK_VALIDATION, please install libelf-dev, libelf-devel or elfutils-libelf-devel")
+ SKIP_STACK_VALIDATION := 1
+ export SKIP_STACK_VALIDATION
+ endif
+endif
+
ifeq ($(KBUILD_EXTMOD),)
core-y += kernel/ certs/ mm/ fs/ ipc/ security/ crypto/ block/
@@ -1035,18 +1047,6 @@ prepare0: archprepare gcc-plugins
# All the preparing..
prepare: prepare0 prepare-objtool
-ifdef CONFIG_STACK_VALIDATION
- has_libelf := $(call try-run,\
- echo "int main() {}" | $(HOSTCC) -xc -o /dev/null -lelf -,1,0)
- ifeq ($(has_libelf),1)
- objtool_target := tools/objtool FORCE
- else
- $(warning "Cannot use CONFIG_STACK_VALIDATION, please install libelf-dev, libelf-devel or elfutils-libelf-devel")
- SKIP_STACK_VALIDATION := 1
- export SKIP_STACK_VALIDATION
- endif
-endif
-
PHONY += prepare-objtool
prepare-objtool: $(objtool_target)
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index e79f15f108a8..ad0118fbce90 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -346,6 +346,7 @@ SECTIONS
/DISCARD/ : {
*(.eh_frame)
*(__func_stack_frame_non_standard)
+ *(__unreachable)
}
}
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 0444b1336268..f457b520ead6 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -195,6 +195,17 @@
#endif
#endif
+#ifdef CONFIG_STACK_VALIDATION
+#define annotate_unreachable() ({ \
+ asm("%c0:\t\n" \
+ ".pushsection __unreachable, \"a\"\t\n" \
+ ".long %c0b\t\n" \
+ ".popsection\t\n" : : "i" (__LINE__)); \
+})
+#else
+#define annotate_unreachable()
+#endif
+
/*
* Mark a position in code as unreachable. This can be used to
* suppress control flow warnings after asm blocks that transfer
@@ -204,7 +215,8 @@
* this in the preprocessor, but we can live with this because they're
* unreleased. Really, we need to have autoconf for the kernel.
*/
-#define unreachable() __builtin_unreachable()
+#define unreachable() \
+ do { annotate_unreachable(); __builtin_unreachable(); } while (0)
/* Mark a function definition as prohibited from being cloned. */
#define __noclone __attribute__((__noclone__, __optimize__("no-tracer")))
diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h
index f7350fcedc70..a59e061c0b4a 100644
--- a/tools/objtool/arch.h
+++ b/tools/objtool/arch.h
@@ -31,9 +31,8 @@
#define INSN_CALL_DYNAMIC 8
#define INSN_RETURN 9
#define INSN_CONTEXT_SWITCH 10
-#define INSN_BUG 11
-#define INSN_NOP 12
-#define INSN_OTHER 13
+#define INSN_NOP 11
+#define INSN_OTHER 12
#define INSN_LAST INSN_OTHER
int arch_decode_instruction(struct elf *elf, struct section *sec,
diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 039636ffb6c8..6ac99e3266eb 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -118,9 +118,6 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
op2 == 0x35)
/* sysenter, sysret */
*type = INSN_CONTEXT_SWITCH;
- else if (op2 == 0x0b || op2 == 0xb9)
- /* ud2 */
- *type = INSN_BUG;
else if (op2 == 0x0d || op2 == 0x1f)
/* nopl/nopw */
*type = INSN_NOP;
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index e8a1f699058a..5fc52ee3264c 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -51,7 +51,7 @@ struct instruction {
unsigned int len, state;
unsigned char type;
unsigned long immediate;
- bool alt_group, visited;
+ bool alt_group, visited, dead_end;
struct symbol *call_dest;
struct instruction *jump_dest;
struct list_head alts;
@@ -330,6 +330,54 @@ static int decode_instructions(struct objtool_file *file)
}
/*
+ * Find all uses of the unreachable() macro, which are code path dead ends.
+ */
+static int add_dead_ends(struct objtool_file *file)
+{
+ struct section *sec;
+ struct rela *rela;
+ struct instruction *insn;
+ bool found;
+
+ sec = find_section_by_name(file->elf, ".rela__unreachable");
+ if (!sec)
+ return 0;
+
+ list_for_each_entry(rela, &sec->rela_list, list) {
+ if (rela->sym->type != STT_SECTION) {
+ WARN("unexpected relocation symbol type in .rela__unreachable");
+ return -1;
+ }
+ insn = find_insn(file, rela->sym->sec, rela->addend);
+ if (insn)
+ insn = list_prev_entry(insn, list);
+ else if (rela->addend == rela->sym->sec->len) {
+ found = false;
+ list_for_each_entry_reverse(insn, &file->insn_list, list) {
+ if (insn->sec == rela->sym->sec) {
+ found = true;
+ break;
+ }
+ }
+
+ if (!found) {
+ WARN("can't find unreachable insn at %s+0x%x",
+ rela->sym->sec->name, rela->addend);
+ return -1;
+ }
+ } else {
+ WARN("can't find unreachable insn at %s+0x%x",
+ rela->sym->sec->name, rela->addend);
+ return -1;
+ }
+
+ insn->dead_end = true;
+ }
+
+ return 0;
+}
+
+/*
* Warnings shouldn't be reported for ignored functions.
*/
static void add_ignores(struct objtool_file *file)
@@ -843,6 +891,10 @@ static int decode_sections(struct objtool_file *file)
if (ret)
return ret;
+ ret = add_dead_ends(file);
+ if (ret)
+ return ret;
+
add_ignores(file);
ret = add_jump_destinations(file);
@@ -1037,13 +1089,13 @@ static int validate_branch(struct objtool_file *file,
return 0;
- case INSN_BUG:
- return 0;
-
default:
break;
}
+ if (insn->dead_end)
+ return 0;
+
insn = next_insn_same_sec(file, insn);
if (!insn) {
WARN("%s: unexpected end of section", sec->name);
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